1. Field of the Invention
The present invention relates to an optical apparatus such as an image pickup apparatus and an interchangeable lens, and particularly to an optical apparatus in which an optical element such as a lens is moved by a motor.
2. Description of the Related Art
In such an optical apparatus, when the motor moves the optical element, rotation unevenness (vibration) of the motor caused due to manufacturing errors thereof generates noise to increase motor drive sound.
Japanese Patent No. 2918183 discloses a method for reducing vibration of a stepping motor caused due to manufacturing errors thereof. Specifically, the method stores in a memory, for each of error ranks predetermined based on amount of an electric angle error between excitation phases of the stepping motor, an electric angle correction value corresponding to the electric angle error amount. Then, the method reads from the memory the electric angle correction value corresponding to the error rank of each stepping motor, and changes switching timings of the excitation phases of that stepping motor by the electric angle correction value to correct a phase of an excitation current applied to each excitation phase, thereby reducing the vibration of the stepping motor.
However, the vibration reduction method disclosed in Japanese Patent No. 2918183 needs to predetermine the error ranks of the individual stepping motors based on the electric angle error amount between the excitation phases. Methods to obtain the electric angle error amount include measuring arrangement dimensions of stator pole teeth by using a precision scale or by measuring a vibration amount of an actually driven motor to evaluate (calculate) the electric angle error amount based thereon, any of which needs measurement or calculation for each motor.
In addition, since the vibration reduction method disclosed in Japanese Patent No. 2918183 predetermines the error rank of each motor, even when characteristics of the motor change with time, the change is not corrected. Therefore, the vibration reduction method cannot always use a proper correction value.